US 3587098 A
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United States Patent Filed Inventor Appl. No.
Patented Assignee LIGHTWEIGHT REFLECTING MATERIAL FOR RADAR ANTENNAS -9 Claims, 4 Drawing Figs.
US. Cl 343/915 Int. Cl ..1-10lq 15/20 Field of Search 343/840, 872, 897, 915
References Cited UNITED STATES PATENTS Mcllroy et al. Price R0ttmayer.. Pessin Tipton Primary Examiner-Eli Lieberman Attorneys-R. S. Sciascia, T-. E. Hodges and W. F. McCarthy ABSTRACT: A lightweight R.F. reflecting material for an inflatable antenna comprising a laminate of Mylar-aluminum foil-Dacron leno weave-aluminum foil-Mylar.
POLYESTER FILM ALUMINUM FOIL ALUMINUM FOIL POLYESTER FILM DACRON LENO WEAVE MATERIAL PATENTEDJUHZZIHYI 3 5 7,09
POLYESTER FILM l4 ALUMINUM FOIL DACRON LENO WEAVE MATERIAL l8 ALUMINUM FOIL 2 POLYESTER FILM INVENTOR .F/G. 4. F7613.
CHARLES N. GOSNELL ATTORNEY LIGHTWEIGHT REF LECTING MATERIAL FOR RADAR ANTENNAS The present invention relates to the structure of fabric used in an inflatable antenna, and more particularly relates to a laminated fabric which is used in constructing the parabolic reflector of an inflatable antenna.
The best prior art material was a glass cloth, coated with silver powder and covered with a vinyl facing. However, the glass cloth is heavy, and the final composite weighed 15 to 17 ounces per square yard. Additionally, glass yarns are adversely sensitive to folding, so a stronger and heavier cloth was required to compensate for weakening of the fabric due to bending.
The general purpose of this invention is to provide an RF. reflective material for an antenna which is lightweight, resists weakening due to folding, has a low tendency to elongate under the loads imposed on it, is very flexible, has excellent reflectivity, even after severe handling and folding, and has good tear and rip resistance. To attain this, the present invention provides a laminated fabric, the typical construction of which is organic film-metallic film-woven material-metalic film-organic film.
The exact nature of this invention as well as other advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings in which:
FIG. ll illustrates a diagrammatic view of the laminate structure of the fabric;
FIG. 2 shows a diagrammatic view of a modification of the invention.
FIG. 3 illustrates the structure of FIG. 2 in a parabolic reflector.
FIG. 4 is a side view of FIG. 3.
In the selection of a material for construction of an inflatable antenna, an important factor to be considered is the strength to weight ratio of the material. This ratio is a paramount consideration since the major reason for the existence of an inflatable antenna is its very light weight in comparison to an equivalent rigid antenna. Another important consideration is the dimensional stability of the material, since the material will .have sustained loads imposed on it due to the inflation of the antenna. A reasonable degree of elongation would be acceptable in a radome material because its dimensional requirements are not critical. However, a good lens material should have relatively low elongation since it is required to balance and position loads on the frame of the reflector. In addition, the reflector material should have very low elongation at its design loading because a secondary type of elongation, known as creep, could introduce an uncontrolled dimensional change and cause the parabolic reflector to change its shape. This type of change could defocus the reflector and cause a marked degradation in antenna performance. The selected material must also be flexible so the antenna may be folded for compact stowage prior to inflation, but the folding should not degrade either the strength or the reflectivity of the material. Additionally, the material should have a high resistance to both the initial starting of a tear and tear propagation, once the rip has been initiated.
Referring to FIG. 1 in which the preferred embodiment is illustrated, there is shown a laminated fabric which has as its exterior coatings organic polyester films I2 and 20, which may be Mylar. Beneath each of the exterior coatings l2 and 20 are layers of aluminum foil 14 and 18, and sandwiched in between the aluminum foil layers 14 and 18 is a Dacron leno weave material 16. The organic films l2 and 20 have good dimensional stability and a high strength to weight ratio. They also have high resistance to the initial starting of a tear, but once the tear is initiated, they have very low resistance to tear propagation. The open weave material, which in the preferred embodiment is a Dacron leno weave, rectifies this deficiency of the polyester films, and effectively resists tear propagation.
The addition of the open weave material has the additional advantage of allowing much thinner and lighter organic films to be used, since the material will carry a good portion of the loading due to inflation of the antenna. Polyester fibers of Dacron were chosen as the yarn for the leno weave materials since they are not damaged by folding. Aluminum foil was chosen as the reflective material because of its light weight. Alternatives, such as a fine silver pigment in a polyester resin base, are undesirable because of their relatively heavy weight.
The preferred laminate is constructed in the following manner: 0.000] 8 inch aluminum film isjoined to 0.00035 inch Mylar to form a sublaminate. Two pieces of this sublaminate are then sandwiched around 0.6 ounce per square yard, 12X4 count, high tenacity Dacron leno weave, with the Mylar faces being on the outside of the finished laminate. The sublaminates are joined to the leno weave material by adhesive bonding, although thermal heat sealing or dielectric sealing might also be used. The finished laminate is very light weight, at less than 3.6 ounces per square yard, and has a power reflectivity of greater than 97 percent.
The material for the radome and lens, which do not require R.F. reflectivity, was chosen to be a 12x4 count high tenacity Dacron leno weave laminated between two 0.25 mil Mylar films.
Referring to FIG. 2, a second embodiment of the invention is illustrated. A pattern of Litz wire, with wires 24 running perpendicular to wires 22, is laminated between two plastic films 26 and 28, which may be Mylar. The wires 24 and 22 may be woven as if the Litz wires were conventional textile yarns, or may simply be laid together in a rectangular pattern without weaving. Dimensional stability is high since the wire carries most of the load imposed on the laminate, and the laminate is not adversely effected by folding since the fine strands which comprise each individual Litz wire bend easily without kinking.
FIG. 3 illustrates a front view of a parabolic reflector 30, while FIG. 4 illustrates a side view of the same reflector 30. The reflector is composed of I2 gores of laminated material joined at seams 32. One important construction feature to be noted is that one set of the Litz wires, either 22 or 24, must run in the direction of polarization of the radar beam being tracked.
A lightweight R.F. reflective material has been disclosed which folds easily without weakening, has good dimensional stability, has excellent reflectivity, even after severe handling, and is resistant to tearing. Obviously, many modifications and variations are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically disclosed.
ll. A lightweight radio frequency reflective laminate for use in a collapsible antenna comprising:
a first polyester film as a protective outer layer on one side of said laminate;
a second polyester film as a protective outer layer on the other side of said laminate;
said first and second polyester films providing the laminate with good dimensional stability and a high strength to weight ratio;
an open weave of Dacron Yarn material sandwiched between said first and second polyester film said Dacron material providing good dimensional stability, a high strength to weight ratio, and also resistance to tear propagation;
at least one layer of radio frequency reflective aluminum material adjacent said Dacron material and also sandwiched between said first and second polyester films;
said first and second polyester films, said Dacron material and said aluminum reflective material all being joined together to form a unitary laminate.
2. A lightweight radio frequency reflective laminate as set forth in claim 1 wherein:
said open weave material has a leno weave.
3. A lightweight radio frequency reflective laminate as set forth in claim 2 wherein:
said at least one layer ofradio frequency material comprises a thin layer of aluminum foil. 4. A lightweight radio frequency reflective laminate as set forth in claim 3 wherein:
each of said first and second polyester films is comprised of Mylar. 5. A lightweight radio frequency reflective laminate as set forth in claim 4 wherein:
said at least one layer of radio frequency reflective aluminum foil comprises two layers, each of which is sandwiched between said Dacron leno weave material and one of said layers of Mylar. 6. A lightweight radio frequency reflective laminate as set forth in claim 5 wherein:
each of said layers of aluminum foil is 18 mils thick; each of said layers of Mylar is 35 mils thick; and
said Dacron leno weave material is 0.6 ounces per square yard and is l2 4 count. 7. A lightweight radio frequency reflective laminate as set forth in claim 6 wherein:
said laminate composes the reflector ofa collapsible antenna. 8. A lightweight radio frequency reflective laminate as set forth in claim 1 wherein:
said at least one layer of radio frequency reflective material comprises two layers of material, each of which sandwiched between said open weave material and one of said layers of polyester film. 9. A lightweight radio frequency reflective laminate as set forth in claim 8 wherein:
said laminate composes the reflector ofa collapsible anten-